M. Mathews discloses in U.S. Pat. No. 3,819,861 apparatus for enhancing the sound quality of musical instruments. Electrical signals representative of sound are modulated in a predetermined manner to increase their spectral content and are then processed by a resonance network which alters the amplitude and phase relationships of the various harmonic signal components. The processed signals are then demodulated with the method re-creating a distorted replica of the original tone which is rich in harmonics that are uncorrelated in amplitude and in phase with each other. This patent, amongst other things, fails to show the control of amplitudes of the different frequencies and, consequently, is unlike the invention disclosed herein.
R. Deutch shows in U.S. Pat. No. 3,913,442 a computer organ of the type wherein a musical wave shape is synthesized by computing in real time the amplitude contributions of the constituent Fourier components and summing these to obtain each wave-shape sample point amplitude, the tonal quality or voice of the produced note being established by a set of harmonic coefficients that specify the relative amplitude of each Fourier component. Circuitry is disclosed for modifying the harmonic coefficient values to accomplish transient voice insertion including "chiff" and percussive transients to modulate the harmonic content as a function of time during attack and decay and to facilitate the external insertion of additional voices for the instrument. This circuitry is restricted to the keyboard and cannot handle outside signals, as a consequence whereof it is unlike the circuitry contemplated within the scope of the present invention.